1. Field of the Invention
This invention relates to an apparatus and method for treating one side of a web of film, fabric or other material with a flowable treatment material.
2. Description of the Prior Art
Treatment of both sides of a moving web is commonly practiced in the textile and other industries. The method most widely used involves dipping a loop of the web into a bath of treating material. Exemplary of the art is U.S. Pat. No. 2,878,778 of Kusters, in which both sides of a web of film are treated by submergence in a dye-containing container.
Occasions arise where only one side of a web is to be treated. Examples of such one side treatments include the application of an adhesive to a fabric or film, spreading of a monolayer of granular material onto a web, and imbibition dyeing of one side of a plastic film. Use of dip tanks is contraindicated when the treatment is to be limited to a single side of the web.
In some prior art one side coating processes, the treating material is discharged from a spreader nozzle directly onto the web surface in a thin layer. Generally, such application results in an overflow of excess treating material from the edges of the web. Troughs or other means are required to catch the overflow for recycle or disposal.
In the graphics arts field, the dyeing of one side of a plastic film has usually been accomplished by hand spreading the dye solution. Often, the resulting depth of color saturation is too uneven to meet the specific requirements, and the colored film must be discarded.
The dyeing process may simply comprise application of a dye coating which adheres to the film surface. On the other hand, imbibition dyeing involves imbibition of the dye solution into the film itself, and the remaining dye solution on the film surface is subsequently removed. The colorant becomes a part of the film structure as the dye solvent is evaporated.
In imbibition processes, the time of exposure to the treating material may be critical, particularly if absorption must be limited to a fraction of the web thickness. Such is the case, for example, when a web has an internal or external layer which is sensitive to the treating material. Common examples of such layers in webs are adhesives joining multilayered films, foam backing, photographic emulsions, and the like.
Removal of treating material from the web surface following the desired uniform treatment time avoids the deleterious results of overtreating or undertreating parts of the web. Hand application of rapidly imbibed dye solutions on films is often impractical because uneven coloration cannot be avoided.